Amorphous and polycrystalline solar cells are limited in their efficiency to convert light into energy. Single crystal high mobility materials are capable of much higher efficiency, but are typically much more expensive. Conventional equipment is designed for semiconductor applications with extreme requirements and with a very high cost involved. However, these systems all have high cost and are not capable of high throughput automation.
To achieve very low cost epitaxial deposition for photovoltaic applications at high throughput, the inventors believe that a radical change is required rather than simply making everything larger. For example, the inventors have observed that batch reactors are limited in throughput with high cost of materials, consumables, and automation challenges. Very high flow rates of hydrogen, nitrogen, water, and precursors are also required. Furthermore, a large amount of hazardous byproducts are generated when growing thick films.
Continuous reactors have been attempted many times for epitaxial processes but have never been production worthy nor achieved good precursor usage. The major issue is poor film quality and excessive maintenance.
On the other hand, single wafer reactors have very inefficient utilization of precursors and power (electrical) and have lower per wafer throughput. Plus single wafer reactors need complex substrate lift/rotation mechanisms. Thus, although single wafer reactors can have very high quality, low metal contamination levels, and good thickness uniformity and resistivity, the cost per wafer is very high to get these results.
Therefore, the inventors have provided embodiments of a substrate processing tool that may provide some or all of high precursor utilization, simple automation, low cost, and a relatively simple reactor design having high throughput and process quality.